Magnetic-field-producing device



Feb. 10, 1959 M. F. REYNST 2,873,413

MAGNETIC-FIELD-PRODUCING DEVICE Filed Nov. 30. 1955 4 INVENTOR.

M. F. HEYNST AGEQT United States Patent l 2,873,413MAGNETIC-FIELD-PRODUCING DEVICE Maximilian Felix Reynst, Eindhoven,Netherlands, assignor, by mesne assignments, to North American PhilipsCompany, Inc., New York, N. Y., a corporation of Delaware ApplicationNovember 30, 1955, Serial No. 550,115

Claims priority, application Netherlands December 4, 1954 directlythrough a comparatively large range by means of a rotational movement.The device according to the invention is characterized in that anannular soft-iron disc is arranged between the magnets and co-axiallytherewith, at least one edge of the disc having a particular profile forcontrolling the magnetic flux, co-operating with a likewise profiledsubstantially annular and coaxial softiron pole-piece, in such mannerthat the flux in the gap between the profiles flows substantiallybetween the magnetic rings. The cooperating parts are preferablyprovided with adjacent toothed portions with the same pitch of teeth.

It may be mentioned that devices for controlling a mag netic flux bymeans of relatively movable teeth are known per so. However, the controlrange obtainable therewith is limited, as will be explained hereinafter.

In order that the invention may be readily carried into effect, it willnow be described, by way of example, with reference to the accompanyingdrawing, in which Figs. 1 and 2 show an embodiment, one half in axialsection and cross-section, respectively, and the other half in side viewand elevation view, respectively.

Fig. 3 shows a slightly modified construction in axial section and Fig.4 shows a detail of another variant.

Figs. 1, 2 and 3 show a magnetic electron lens which may surround theneck of a cathode-ray tube 1 (not shown further). The lens substantiallycomprises two flat rings 3 and 5 which are axially magnetizedand-consist of permanent magnetic material, preferably ceramic materialof the kind described in British Patent No. 798,127. The two rings 3 and5 are, co-axially arranged side by side with the poles of likepolarity-in this case the north polesadjacent one another. Arrangedcoaxially between the two rings 3 and 5 is a substantially annular disc7 of soft iron (this is to be understood to include not only soft ironbut also all materials having the same magnetic properties as soft iron,such as nickel, ferrites, etc). The assembly 3, 5, 7, is externallycovered with two soft-iron discs 9 and 11, constituting flanges on twoshort soft-iron pieces of tube 13 and 15.

The inner edge of disc 7 is provided with teeth 17 and concentricallyembraces a soft-iron disc 19 constituting a flange on a mately the samediameter as that of the tube pieces 13 and 15. The flange 19 externallycomprises the same number of teeth (indicated by 23) as the disc 7,which teeth thus have the same pitch as the teeth 17 and in the positionshown are in opposition to said teeth (that is to say'in straightopposition). The disc 7 is externally provided with teeth 25, the numberand the pitch of which are thus equal to those of the teeth 17 and 23.

short soft-iron piece of tube 21 of approxi-.

The disc 7 and the magnets 3 and 5 are coaxially surrounded by asoft-iron piece of tube 27 comprising teeth 29 and 31 on the two edgesand a series of windows 33 provided centrally on its circumference. Theseries of teeth 29 and 31 are in opposition to series of teeth 35 and 37formed on the edges of the flanges 9 and 11. The numbers and the pitchesof all these teeth and windows are equal to those of the teethpreviously described.

Magnetic fields occurs between the piece of tube 21 and the pieces oftube 13, 15, which fields may be used in known manner for concentratingan electron beam passing through the neck of the tube I. Said fieldsextend wholly symmetrically with respect to the disc 7 and for the sakeof convenience only the field at the left of the disc will be consideredmore fully hereinafter. Part of the fiux-represented by a line of force41--flows, starting from the magnet 3, directly via the piece of tube21. A larger portion-represented by two lines of force 43 and 45flowsvia the teeth 17 and 23 and across their separating air-gap; the extentof this portion is greatly dependent upon whether the teeth 17 and 23are in opposition or not. At the position shown (see Fig. 2), the teeth17 and 23 are in straight opposition and it will be evident that at thisposition the gap is at a minimum and the magnetic reluctance in thecircuit of the lines of force 43, 45 is minimum, and maximum at theposition at which the parts 7 and 19 have been turned through an angleor equal to the half pitch of the teeth. The magnetic fiux in the neckof the tube 1 is as great and as small as possible at the said twopositions, it thus being possible to corn trol the flux (and the fieldstrength) by turning the part 7 or 19 relative to the other.

In know control devices with gearings, it has been found that thecontrol range is greatly limited by the fact that at the position ofminimum field strength a considerable stray flux laterally (axially)emerges from and enters the toothed discs. Consequently the minimumfield strength is usually only slightly lower than the maximum fieldstrength. According to the invention, said disadvantage is obviated inthat (see Fig. 1) the flux which passes from the disc 7 via the teeth 17and 23 to the disc 19 (lines of force 43 and 45) flows between themagnets 3 and 5, i. e., this variable flux path is located between themagnets 3 and 5. Lateral (axial) emergence of the lines of force fromthe face areas of the discs is prevented owing to the faces of themagnets 3 and 5which are the sources of the lines of forcebeingpositioned in facing relation to the discs, so that at the minimumposition (non-opposition of the teeth 17 and 23) the said flux isgreatly decreased and hence a large control range (a variation of 1:2and more) can be achieved.

Another possibility of control-which may also be used separately-isprovided by the co-operation of the teeth 25 on the outer edge of disc 7with the ring 27 provided with the windows 33, since part of the flux ofthe magnet 3 (see line of force 47 in Fig. 1) may flow along a parallelpath via the ring 27 and the flange 9 and thus be largely extracted fromthe useful flux traversing tube 1. By turn ing one of the elements 7 and29 with respect to the other, the parallel flux is controlledfundamentally in the same way as the flux 43, 45, but in the oppositesense, sincesee Figs. 1 and 2-the position of non-opposition of theteeth 25 and the bridge pieces 49-which in this case are to be regardedas teethcoincides with the position of opposition of the teeth 17 and23. In this case also lateral emergence of the lines of force from thedisc 7 is prevented or at least substantially suppressed by the mag nets3 and 5.

The magnetic connection between the flange 9 (or 11) and the ring 27extends in the case shown via teeth 35 and 29 (and 37, 31) formed onsaid parts. The magnetic reluctance resulting from said transition is inseries with that resulting from the teeth 25 and 49 and is controlled Iin the same sense. Theadditional variation thus obtained is not great,since lines of force (for example line of force 51) can laterally enterthe flange 9, but it assists in the variation brought about by the teethand bridge pieces 25 and '49.

As a matter of fact (see Fig. 3), the ring 27 may have inwardly directedteeth 53 to substitute the bridge pieces 49. On the other hand, it ispossible for windows 55 cooperating with the teeth 17, similar to thewindows 33 in the part 27 (as shown in Fig. 1) and the teeth 25 in thedisc 7, to be provided in the piece of tube 2-1. In the embodiment shownin Fig. 3, the edges of the'fianges 9, 11 and those of the ring 27 arenot provided with teeth.

' lnorder to facilitate the relative rotation of the various partsrequired for the control, it is possible (see Fig. 3) tosecure the parts9, 3, 7, 5, 11 together, to secure the piece'of tube 21 to the tube '1(or to a separate nonmagnetic supporting pipe surrounding it) and tosecure the ring 27 to the chassis'of the apparatus of. which thedescribed device forms part, while the tube pieces '13 and 15 can rotateabout the tube 1. The control is'then effected by rotating the assembly9, 3, 7; 5, 11 while the rings 21 and 27 remain at rest. 7

Fig. 4 shows a profile of amodification of the discs 7 and 21 which maybe used, for example instead of the teeth 17 and 23.

What is-claimed is:

1. A magnetic-field-producing. device comprising two, annular, coaxial,closely spaced, permanent magnets each magnetized in its axial directionso that like poles face each other, a first annular soft ferromagneticmember disposed between and coaxially with the two magnets, and a secondannular soft ferromagnetic member arranged coaxially relative to' themagnets and adjacent the first soft ferromagnetic member and themagnets,said first and second soft ferromagnetic members having portions facingeach other in a radial direction and defining an airgap therebetween andforming, in accordance with their relative positions, reluctance pathsof different magnitude, said air-gap being located substantially betweensaid two magnets and lying substantially within an area encompassed bythe outer and inner diameters of the annular magnets, said first andsecond soft ferromagnetic membersbeing relatively movable so as to'varythe reluctance path for the flux produced by said magnets,'wherebymagnetic fields with a wide range of intensities are obtainable.

2. A device as set forth in claim 1, wherein thefirst and second softferromagnetic members have facingtoothed portions of the same pitch.

3; A'device producing: a'variable permanent magnetic field, comprising apair of continuous, annular, coaxial, closely spaced, permanent magnetseach magnetized in its axial direction producing poles of like polarityon facing surfaces, a first annular soft ferromagnetic member mountedbetween, abutting and coaxially with the two magnets and a secondannular soft ferromagnetic mem- =bert arranged coaxially with the tWOmagnets and within and substantially coplanar with'the first member,said first-and second members having radially-extending, facing, toothedportions of the same pitch defining an annular space lying between andadjacent the magnets and substantially within the spacebounded by themagnets, said two members being relatively axially rotatable to therebyvary the reluctance path for flux produced by the magnets and thereby.vary the strength of an internally-produced permanent magnetic field.

4. A device producing a variable permanent magnetic field, comprising apair of continuous, annular, coaxial, spaced, permanent magnets eachmagnetized in its axial direction producing poles of like polarity onfacing surfaces, said magnets being spaced apart a distance smaller thantheir radial thickness, a first annular soft ferromagnetic membermounted between, abutting and coaxiallywith the'two magnets, and asecond annular soft ferromagnetic member arranged coaxially with the twomagnets and substantially coplanar with the first member, said firstmember having a radially-extending, toothed portion, said second-memberhaving a plurality of circumferentially-arranged apertures aligned with,facing, and of the same p'it'ch as the, teeth on the toothed portion anddefining between the two members air-gaps, the airgaps between thefacing portions of the first and second members being locatedsubstantiallydirectly between the pair of magnets, said two membersbeing relatively axially rotatable to thereby vary the reluctance pathfor fiux produced by the magnets and thereby vary the strength of aninternally-produced permanent magnetic field.

5. A device producing a variable permanent magnetic field, comprising apair of continuous, annular,'coaxial, spaced,,permanent magnets eachmagnetized in its axial direction so that like, poles face one another,a first annular soft ferromagnetic member mounted between, abuttingandcoaxially with the two magnets, said first member having inner and outerradially-extending toothed portions of thesame given pitch, a secondannular soft ferromagnetic member arranged coaxially with, within,abutting and substantially coplanar with the first member, said secondmember havingv a radially-extending toothed portion'of said given pitchcooperating with the inner toothed portion of said first member todefine reluctance paths for the-flux produced by said magnets, and athird annular soft ferromagnetic member arranged coaxially with thefirst and second members, saidthird member having a toothed portion ofsaid given pitch cooperating with the outer toothed portion of saidfirst member to define reluctance paths for-the flux produced by saidmagnets, said first member being rotatable relative to said second andthird-members to thereby change the reluctance paths for the fluxproduced by said magnets and thereby vary the strength ofaninternally-produced permanent magnetic field.

6. A device asset forth in claim 5 wherein the first, second -and thirdmembers are so arranged that the cooperating toothedportions of thefirst and second members are aligned when the cooperating toothedportions of the first and third members are misaligned.

7. A device as set forth in claim 4 wherein the second member abuts themagnets.

References Cited in the file of this patent UNITED STATES PATENTS2,333,230 Beechlyn Nov. 2,-1943 2,369,769 Ramb'er'g Feb. 20, 19452,608,665 Parker Aug. 26, 1952 2,714,678 Wolff Aug. 2, 1955 2,740,064Birkbeck Mar. 27, 1956

